1. Field of the Invention
The present invention relates to a toll collection system in a toll road for vehicles and, more particularly, to a vehicle measuring apparatus using a laser sensor suitably applied to the system.
2. Description of the Background Art
Recently, attempts to introduce an intelligent traffic system are being made throughout the world. For example, an electronic toll collection system (abbreviated as ETCS), an automatic toll collection system is being introduced which is capable of reducing product delivery cost and an environment pollution through mitigation of vehicle congestion in tollgate as occurring in the current manual Toll Collection System (abbreviated as TCS), and reducing operation and maintenance cost and improving a service through a toll collecting automation.
The electronic toll collection system is collecting a toll by using a Dedicated Small Region Communication (abbreviated as DSRC) wirelessly while a vehicle is running without stop when the vehicle passes a tollgate. However, with only the wireless communication, there is no way to discriminate a toll paid vehicle and a non-paid vehicle. For example, if a large bus equipped with an OVU (On Vehicle Unit: a terminal installed in a vehicle for a radio communication and toll payment) of a small-scale car passes the automatic toll payment system, it is not discernible whether a small car has passed the system or a large bus has passed the system.
Thus, in order to improve such a problem, a car classification device to classify the car and the DSRC for the radio communication are required.
The car classification device detects a violated car and a normal car by measuring at least a height and a width of a car travelling on a road out of a width, a height and a length, discriminating the type of the car by using the measurement result and checking the car type information and radio communication information. Here, the violated car can be a large bus equipped with an OVU of a small car.
The car classification device for vehicles travelling on the road is divided into a contact type and a non-contact type depending on whether it contacts a detection target. The contact type is to classify a type of car by using a pressure of a wheel of the car, while the non-contact type uses a photo sensor, a CCD (Charge Coupled Device) camera or a laser sensor in its classification.
The conventional contact type vehicle measuring apparatus will now be described with reference to FIG. 1.
FIG. 1 is a perspective view of a vehicle measuring apparatus using a tread-board sensor.
As shown in FIG. 1, the contact type vehicle measuring apparatus includes a resistor contact type tread-board sensor. The tread-board sensor 110 is buried under the surface of the road on which the vehicle travels and measures a change of resistance according to a wheel pressure of the running vehicle, to thereby measure the number of wheel shafts, a distance from front wheels to rear wheels, a distance between front wheels or rear wheels, so called wheel width, to classify the vehicle type.
However, with the conventional contact type vehicle measuring apparatus using the tread-board, it is impossible to measure a vehicle travelling faster than a certain velocity. In addition, in order to guide the vehicle to pass the surface in which the tread-board is buried, an induction facility such as a traffic island should be installed, for which thus an installation space should be provided on the road.
A non-contact type vehicle measuring apparatus to improve the problem of the contact type vehicle measuring apparatus will now be described with reference to FIGS. 2A and 2B. There are methods for using a photo sensor, a CCD camera and a laser beam for the non-contact type vehicle measuring apparatus.
FIG. 2A illustrates a construction of the non-contact type vehicle measuring apparatus using a photo sensor in accordance with a conventional art.
As shown in FIG. 2A, the non-contact type vehicle measuring apparatus using the photo sensor uses a photo sensor in which a light emitting unit and a light receiving unit are separately constructed. That is, the light emitting unit 211 and a light receiving unit 212 constituting the photo sensor are installed a both sides or upside and downside of the road to measure vehicles according to shielding of a light signal by the vehicle. However, the non-contact type vehicle measuring apparatus using the photo sensor does not possibly measure a height or a width of the vehicle but sense only the entry of a vehicle, and as such, it is not usable for a vehicle type classification and toll collection system.
FIG. 2B illustrates a construction of another non-contact type vehicle measuring apparatus using a photo sensor in accordance with a conventional art.
As shown in FIG. 2B, another non-contact type vehicle measuring apparatus uses a photo sensor with a light receiving unit and a light emitting unit constructed as one body. This non-contact type vehicle measuring apparatus includes a few photo sensors 221 installed with predetermined intervals on a gantry 223 to face the ground and a detection line 222 drawn in a predetermined pattern on the road corresponding to the photo sensors 221. Since a reflection light changes sensitively over a color of a subject due to characteristics of the light signal, the non-contact type vehicle measuring apparatus is operated not to measure the reflection light reflected from an entering vehicle but to measure a reflection light of a portion of the detection line 222 which is not shaded by the vehicle.
Thus, the non-contact type vehicle measuring apparatus measures the width of the vehicle by using the reflection light difference form the detection line 222 between when the vehicle is in absent and when the vehicle passes. In this respect, the detection line 222 can be constructed with a pattern region such as speckled pattern.
However, this non-contact type vehicle measuring apparatus has problems that its accuracy in measurement can be severely degraded if the detection line 222 is damaged or light scatters due to rain or snow.
FIG. 3 illustrates a construction of a vehicle measuring apparatus using the CCD camera in accordance with the conventional art.
As shown in FIG. 3, the vehicle measuring apparatus using CCD camera includes an intermittent marking pattern 312 drawn on the road surface and a plurality of first-dimensional CCD cameras 311 installed with predetermined intervals on the gantry 323 and obtaining a first-dimensional light amount signal from the intermittent marking pattern 312. That is, the vehicle measuring apparatus using CCD camera searches only the shaded portion of the intermittent marking pattern 312 of an image signal obtained by the CCD camera 311 when a vehicle is entering, to detect a vehicle and measure a width of the vehicle.
However, the vehicle measuring apparatus using CCD camera 331 has problems that it can not obtain accurately an image of the vehicle and thus cause a serious measurement error if the intermittent marking pattern 312 is damaged or the amount of light reflected from the intermittent marking pattern 312 changes due to clouds.
Thus, in order to improve an error according to the change of the light amount as described with respect to the apparatus of FIGS. 2A–2B and FIG. 3, a vehicle measuring apparatus using a laser distance sensor will now be described with reference to FIG. 4.
FIG. 4 is a perspective view showing a vehicle measuring apparatus using a laser distance sensor in accordance with the conventional art.
As shown in FIG. 4, the vehicle measuring apparatus using a laser distance sensor includes laser distance sensors 410 installed as many as the number of roadways on the road surface. Each laser distance sensor 410 independently performs a detecting operation to measure a height and a width of a vehicle passing each roadway.
The construction of the laser distance sensor 410 will now be described with reference to FIG. 5.
FIG. 5 is a view showing the construction of the laser distance sensor illustrated in FIG. 4.
As shown in FIG. 5, the laser distance sensor 410 includes a laser emitting/receiving unit 511, a polygonal diffraction lattice for reflecting a laser beam emitted from the laser emitting/receiving unit 511 or a laser beam received after being reflected from an object on the road into several angles while being rotated at a equal speed; and a reflection plate 512 for reflecting the laser beam emitted from the laser emitting/receiving unit 511 or reflecting the laser beam reflected by the diffraction lattices after being reflected from the object on the road to the laser emitting/receiving unit 511.
That is, as for the laser distance sensor 410, since the laser beam is not sensitive to the color of the subject due to the characteristics of laser light and has a straight traveling property, the time taken for the laser beam emitted from the light emitting unit to meet the object, be reflected and come back is measured by the light receiving unit, and then the distance is measured by using the measured time.
The operation of the laser distance sensor 410 will now be described with reference to FIGS. 6A, 6B, 7A and 7B.
FIGS. 6A and 6B show a vehicle detection region using the laser distance sensor of FIG. 5.
FIGS. 7A and 7B are views showing a problem caused when detecting a vehicle by using the laser distance sensor of FIG. 5.
First, in case that the vehicle is normally travelling in the roadway, when the laser emitting/receiving unit 511 irradiates a pulse laser beam emitted from the internal light emitting unit to the diffraction lattice 513 through the reflection plate 512, the laser beam is reflected in a direction by the polygonal diffraction lattice 513. The reflected laser beam is reached on the surface of the vehicle.
Thereafter, the reached laser light is reflected from the surface of the vehicle, which is reached on the light receiving unit of the laser emitting/receiving unit 511 through the reflection plate 512 by the polygonal diffraction lattice 513. At this time, the laser emitting/receiving unit 511 processes the beam reached on the internal light receiving unit and measure a distance for a single point.
After the distance for the single point is completely measured, the diffraction lattice 513 is rotated as much as a predetermined angle.
A laser beam of another pulse emitted from the light emitting unit of the laser emitting/receiving unit 511 is emitted through the diffraction lattice 513 and a reception signal for the laser beam of the emitted pulse is reached onto the light receiving unit of the laser emitting/receiving unit 511 through the diffraction lattice 513, so that a distance for another one point can be measured.
Therefore, by repeatedly performing the operation by rotating the polygonal diffraction lattice 513 which is already aware of the angle from the distance measurement on one of reflection points, it is possible to measure a particular region. In other words, since the vehicle measuring apparatus using a laser distance sensor is a method of irradiating one laser beam to a specific region by using the diffraction lattice 513 in measuring the width of the vehicle, the laser beam has a form of being radiated toward outside on the basis of a starting point, so that the width of the vehicle is measured in the unit of angle as shown in FIG. 6.
In the case that the vehicle type classification reference for the ETCS is provided as the length information such as width, length and height of the vehicle, since the angle value can not be directly used, a process for converting the unit of angle into a unit of length is required. That is, on the assumption that a height from the road surface to the laser distance sensor 410 is h1, a height of the detected vehicle is h2, and an angle of the width of the detected vehicle is ‘r’, a width of the vehicle (w1) is calculated by equation (1) as below:Vehicle width (w1)=(h1−h2)×tangent(r/2)×2 equation  (1).
The width of the vehicle calculated by equation (1) is based on the assumption that an upper width and a lower width of the vehicle are the same with each other.
Accordingly, the vehicle measuring apparatus using the laser distance sensor has the following advantages.
That is, the height and the width of a travelling vehicle can be measured without a slow-moving or stoppage of the vehicle, it is not necessary to widen the road in order to prepare an installation space of an auxiliary unit or a device itself for measuring the vehicle such as the traffic island on the road, a detection line, a pattern or an intermittent marking region are not required on the road, and influence on the measurement of vehicle can be minimized even in a bad weather when it rains or snows.
Nevertheless, the vehicle measuring apparatus using the laser beam has the following problems.
That is, if it is adopted for a large-scale bus, as shown in FIG. 6B, since the width of the upper portion and the width of the lower portion of the vehicle are constant, the width of the vehicle according to the calculation of equation (1) can be determined to the actual width. Meanwhile, however, if equation (1) is adopted to a car to measure the width of the car, as shown in FIG. 6A, since, in general, the width of vehicle is mostly determined at the top point or at the middle point, there is much difference between the width of the top point and the width of the bottom point. Especially, in line with the development of the automobile technology, shapes of cars are in the tendency of diversification. Therefore, conversion of the width of vehicle to length by using information of angle and height may cause much error.
In addition, in case of adopting the conventional vehicle measuring apparatus using laser beam to a multi-lane ETCS, if a vehicle is normally travelling in one roadway, a desired measurement value can be obtained. But if the vehicle travels over two roadways rather than travels in one roadway, the upper middle or lower corner of the vehicle, not the upper both corners of the vehicle, is measured as a width of the vehicle. Then, the measured width of the vehicle would have much difference with an actual width of the vehicle.